1. Field of the Invention
The present invention relates generally to a method of forming an aperture in the dielectric coating of an aluminum circuit card that will allow utilization of the aluminum core to more efficiently dissipate heat generated by an electronic component. such as an integrated circuit device attached thereto. More specifically, the aperture is formed in the aluminum circuit card which allows the integrated circuit device to directly abut the aluminum core, thereby using the core to aid in heat dissipation. The aperture may also be used to provide an electrical contact to the aluminum core of the circuit card.
2. Description of Related Art
It is currently known to use aluminum as a potential reference conductive layer within circuit cards. Typically, an aluminum layer is anodized to form aluminum oxide and then electrophoretically (EP) coated with a polymer material to provide an insulating dielectric layer. Generally, integrated circuit (IC) packages, such as dual-in-line packages (DIP), wire bonded ICs. and surface mount components (SMT) are electrically attached to a wiring layer on the EP polymer layer. These attached chips are then interconnected by the wiring layer also placed on the EP material.
It was noted that a portion of the heat generated by the IC devices was being dissipated through the aluminum core layer but only after the heat was transmitted through the EP polymer and anodized aluminum layer. In this case, the heat was transferred through the entire thickness of both the EP and aluminum oxide layers prior to being dissipated through the aluminum core layer. Thus it can be seen that improvements in thermal efficiency will occur if the integrated circuit devices could be placed in direct contact with the aluminum core. That is, forming an aperture within the aluminum oxide and EP layers having the dimensions of a chip being attached to the card would allow electrical connections to be made between the chip and the wiring on the EP polymer layer while at the same time maintaining direct physical contact with the aluminum core.
U.S. Pat. No. 4,261,792 describes forming an anodized layer over the entire surface of a wafer, etching the anodized layer through a photoresist mask to form an anodized mask layer, and then etching the underlying material using the anodized layer as a mask. U.S. Pat. No. 4,589,961 discusses an improvement to the selective non-anodizing process for fabricating Josephson junction devices by using aluminum oxide as a protective layer. IBM Technical Disclosure Bulletin. "Process For Noble Metal Pattern Generation," discusses a method of generating a noble metal pattern by using a thick anodized aluminum oxide film generating a negative pattern on the oxide using a photoresist step and depositing the desired metal over the entire surface, which includes etching the aluminum oxide. IBM Technical Disclosure Bulletin, "Aluminum-Aluminum Oxide Gas Panel describes fabricating a gas panel using aluminum conductors wherein aluminum is deposited on the gas panel substrate glass. A photoresist conductor pattern is applied and the panel is anodized such that the unprotected aluminum is oxidized and the portion of the aluminum covered by the photoresist remains unoxidized and forms the aluminum conductors. IBM Technical Disclosure Bulletin "Anodization Process for Planarization of Aluminum-Copper-Silicon Metallurgy." is a method for forming conductive pathways of IC interconnections and electrically insulating the pathways by depositing aluminum which is then selectively converted in aluminum oxide, which is a dielectric material. IBM Technical Disclosure Bulletin "Sealing Cracks in Anodized Aluminum with Electrodeposited Organic Material for Dielectric Protection" discusses a technique for placing the EP polymer layer over the anodized aluminum layer of the circuit board. Further U.S. Pat. Nos. 4,898,651 and 4,894,126 describe methods used to anodize the aluminum core layer of a circuit card.
Therefore, it would be desirable to have an aluminum circuit card that will efficiently dissipate the heat generated by integrated circuit devices attached thereto. This is especially important since chips are constantly being developed having a greater number of circuits which generate correspondingly more heat that must be dissipated. Further, a process of forming apertures in the electrically insulating dielectric layers of the aluminum circuit card to allow direct attachment of the chips to the aluminum core would be advantageous.